Cryogenic Pping_Wall Thickness Calculation

1. Your formula is the right form, but not clear. Is SEW one quantity (the material design stress) or are there other factors in there? What is y? I don't have ASME 31.3 to hand but BS 5500 for pressure vessels gives t = P*D_i/(2*S - P) where S = design stress. ASME 31.3 might be a bit different.

You don't give your design stress, but taking a typical figure for steel at room temperature, 170 MPa ~ 25000 psi, t = 0.4 mm isn't far out. But the thickness will be much greater than 0.4 mm for practical reasons, so stress won't be an issue.

2. Not that I'm aware of, but you need to select material which is OK for the low temperature. Carbon steel is no good below about -10°C if I remember right. But according to BS 5500 (an old version, but I don't suppose it's changed much in this respect) austenitic stainless steel is OK down to -196°C, so you shouldn't have a problem finding something suitable, but you need to check.

3. No, see 1 above.

Cheers........Codey

It looks like he has the right material. Sometimes now, carbon steel can get as low as -50 without impact testing.

He still wants SS though. I think the only difference for cold piping is the impact testing right? Design it like normal and then impact test if the design temperature is below what B31.3 recommends.

From memory, most stainless steels are good for either -150 F or -320 F. He'll have to check because I don't remember which ones are good for what. Well, I said he has the right material but I don't see a SA358 TP304 in B31.3. I may have overlooked but most of these pipes have an MDMT of -325 or -425.

There will be other pipe stresses besides the fluid pressure, such as supporting its own and the fluid's weight between pipe supports, thermal expansion/contraction, etc.

I doubt that any 16" o.d., 0.4mm wall product would be described as "pipe," or even "tube"; it's more like "sheet-metal round duct."

SS304 should be fine for the given temperature. I would guess that Schedule 10 (and maybe even 5) would suffice.

just a note for support of your calc.

i have worked on two cryo jobs. all pipe (up to 20") was either sched 5 or sched 10.

You'll probably want to use an ASTM A358 Gr. TP 304L stainless. Schedule 10 weled is good for gas or liquids at -420 deg F (-251 C) to 100 deg F (38 C) and 275 psig. Use 300 lb. weld neck flanges with raised face & Flexittalic gaskets. Also use A320 Gr B8 studs and a194 Gr 8F nuts. Remember not to use carbon nuts/studs due to galvanic (bi-metallic) corrosion

I also think your 0.4mm is the MINIMUM allowable thickness after it's been in service.

The calculated wall thickness is correct, however you should also consider the wall thickness required for external loadings and contraction.